Method and Compositions for Hydraulic Fracturing and for Tracing Formation Water

ABSTRACT

A method of hydraulic fracturing, and tracer composites for use in the fracturing procedure, for tracing the production of formation water from one or more fractured zones. The tracer composites preferably include a formation water tracer material adsorbed onto a solid carrier material.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. patent application Ser. No. 15/133,465 filed Apr. 20, 2016, the disclosure of which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to methods of hydraulic fracturing and to tracer composites which can be used in conjunction with hydraulic fracturing procedures to trace the production of formation water from individual or multiple fractured zones.

BACKGROUND OF THE INVENTION

When conducting a hydraulic fracturing operation, a hydraulic fracturing fluid is pumped into a subterranean formation under sufficient pressure to create, expand, and/or extend fractures in the formation and to thus provide enhanced recovery of the formation fluid. Hydraulic fracturing fluids typically comprise water and sand, or other proppant materials, and also commonly include various types of chemical additives. Examples of such additives include: gelling agents which assist in suspending the proppant material; crosslinkers which help to maintain fluid viscosity at increased temperatures; gel breakers which operate to break the gel suspension after the fracture is formed and the proppant is in place; friction reducers; clay inhibitors; corrosion inhibitors; scale inhibitors; acids; surfactants; antimicrobial agents; and others.

Fracturing operations have long been conducted in both low permeability and high permeability formations in order, for example, to increase the rate of production of hydrocarbon products or to increase the injection rates of water or gas injection wells. Moreover, with the introduction of slickwater fracturing procedures which use large quantities of water containing friction reducers, it is now also possible to stimulate naturally fractured shales by fracturing multiple intervals during staged treatments in horizontal wellbores. Treatment of all zones of interest in a horizontal well may require several hours to a few days to complete.

Water soluble chemical tracers have been used heretofore in hydraulic fracturing operations to trace the return of the aqueous fracturing fluid. These water soluble tracers are intended to dissolve in and flow with the aqueous fracturing fluid.

In a multistage hydraulic fracturing operation, a different chemical tracer can be added to the fracturing fluid used in each of the individual stages. After all of the fracturing stages have been completed, the fluid produced from the well is sampled and analyzed for the presence of the tracers, preferably on a periodic or continuous basis. The detection of one or more of the chemical tracers in the production fluid indicates which of the stages are flowing (i.e., the stages from which the fracturing fluids are returning).

Unfortunately, however, this procedure does not provide significant information as to which of the stages, if any, are producing formation water. Formation water is naturally occurring water which is commonly present in oil and/or gas formations. Formation water salinity levels typically range from 5 to 300 parts part thousand.

The ability to detect and evaluate the production of formation water from the individual stages of a multistage well would be greatly beneficial. Information obtained from such a method could be used to allocate the formation water produced to individual stages. Information from this procedure would also allow an operator to know if certain frac stages have contacted “wet” zones outside the intended target. The operator would then know which interval or frac needs to be shut off to prevent higher than normal formation water production. Tracer data could also help delineate between stage differences in water/oil ratios.

Consequently, a need exists for a procedure capable of (a) distinguishing formation water production from the return of the aqueous fracturing fluid, (b) detecting and determining the flow of formation water from each fracturing stage, and (c) determining the rate of formation water production from each stage or at least the comparative rates of formation water production from multiple fractured zones, particularly in horizontal wells.

SUMMARY OF THE INVENTION

The present invention satisfies the needs and alleviates the problems discussed above.

In one aspect, there is provided a tracer composite for use in tracing the production of formation water. The tracer composite preferably comprises: (a) a solid carrier material which is substantially non-soluble in water and (b) a tracer carried on the carrier material, wherein the tracer preferably is or is formed from a halogenated benzoic aldehyde or a halogenated benzoic acid.

In another aspect, there is provided a tracer composite for use in tracing the production of formation water wherein the composite preferably comprises: (a) a solid carrier material which is substantially non-soluble in water and (b) a tracer carried on the carrier material, wherein the tracer is not substantially eluted from the carrier in water having a salinity level of less than 1 part per thousand by weight but is eluted from the carrier at a rate which increases as the water salinity level increases.

In another aspect, there is provided a method of producing a tracer composite for use in tracing the production of formation water, the method preferably comprising the step of adsorbing a halogenated benzoic aldehyde on a solid carrier material which provides catalytic sites in the presence of water which convert at least a portion of the halogenated benzoic aldehyde adsorbed on the solid carrier material to a halogenated benzoic acid.

In another aspect, there is provided a method of fracturing a subterranean formation, the method preferably comprising the steps of: (a) injecting a fracturing fluid into a fracturing zone of the subterranean formation wherein: at least a portion of the fracturing fluid includes an amount of a tracer composite material, the tracer composite material comprises a tracer on a solid carrier material, the tracer is for tracing the formation water, the carrier material is substantially non-soluble in water, the tracer is or is formed from a halogenated benzoic aldehyde or a halogenated benzoic acid, and the tracer is not substantially eluted from the solid carrier material in water having a salinity level (e.g., a sodium chloride content) of less than 1 part per thousand by weight but is eluted from the carrier at a rate which increases as the water salinity level increases, and (b) analyzing a product recovered from a well associated with the subterranean formation for the presence of the tracer to determine whether the product includes formation water produced from the fracturing zone.

In another aspect of the fracturing method just described, the fracturing zone which is fractured in step (a) is a first fracturing zone and the method preferably further comprises the steps of: (c) injecting, prior to step (b), a fracturing fluid into a second fracturing zone of the subterranean formation wherein: at least a portion of the fracturing fluid injected into the second fracturing zone includes an amount of a second tracer composite material, the second tracer composite material comprises a second tracer on a solid carrier material, the second tracer is for tracing formation water, the carrier material of the second tracer composite material is substantially non-soluble in water, the second tracer is different from said first tracer, the second tracer is or is formed from a halogenated benzoic aldehyde or a halogenated benzoic acid adsorbed on the solid carrier material of the second tracer composite, and the second tracer is preferably not substantially eluted from the solid carrier material in water having a salinity level of less than 1 part per thousand by weight but is eluted from the carrier at a rate which increases as the water salinity level increases and (d) analyzing the product recovered from the well for the presence of the second tracer to determine whether the product includes formation water produced from the second fracturing zone.

Further aspects, features, and advantages of the present invention will be apparent to those of ordinary skill in the art upon reading the following Detailed Description of the Preferred Embodiments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides (1) a method of hydraulic fracturing, (2) tracer composites which can be used in various types of downhole operations for tracing formation water and are particularly well suited for use in the inventive fracturing method, and (3) a method for forming the inventive tracer composites.

The inventive fracturing method and tracer composites can be used in single stage or multistage fracturing operations and are particularly well suited for use in multistage hydraulic fracturing operations such as those conducted in horizontal wells. Using the inventive hydraulic fracturing method and tracer composites, the well operator can determine: (a) whether formation water is being produced from any given fractured zone; (b) how much, or the rate at which, formation water is being produced from the fractured zone; and (c) the comparative formation water production from any given fractured zone versus the other fractured zones in the well.

The inventive tracer composite comprises: (1) a solid carrier material which is preferably non-soluble or substantially non-soluble in water and (2) a tracer which is preferably adsorbed on the solid carrier material. The tracer preferably is not substantially eluted from the solid carrier material in water having a salinity level of less than 1 part per thousand by weight but is eluted from the carrier at a rate which is preferably proportional or substantially proportional to the water salinity level as the salinity level increases.

The initial release of the tracer while being pumped into the fracture can also be further reduced or eliminated by coating the tracer composite with a hydrophobic material. This coating can be a grease or wax. The coating can be applied by heating the coating material to a liquid and spraying onto the tracer/carrier composite as the composite tumbles or in the case where the coating is a solid wax like a paraffin the composite can simply be tumbled with coating material. The coating amount would be preferably 5 to 40% by weight of the resulting coated composite, more preferably about 10%.

It is also preferred that the chemical tracers used in the inventive composite not be substantially soluble in crude oil at 25° C. and 100 kPa.

In addition to the above, the tracer used in forming the inventive composite will also preferably be: (a) chemically stable under the temperature, pressure and other physical conditions to which the tracer will be exposed within the subterranean formation; (b) substantially chemically inert with respect to the other components of the fracturing fluid and to the liquids, solids, and gases within the formation; and (c) analytically detectable at low concentration levels (most preferably in parts per billion).

Examples of tracers preferred for use in the inventive composite include, but are not limited to, halogenated benzoic aldehydes and halogenated benzoic acids. The tracer material used in the inventive composite will most preferably be or be formed from a halogenated benzoic aldehyde. Halogenated benzoic aldehydes suitable for use in the inventive composite include, but are not limited to:

-   2-fluorobenzaldehyde; 4-fluorobenzaldehyde;     2,3,4,5-tetrafluorobenzaldehyde; -   2-(trifluoromethyl) benzaldehyde; 4-(trifluoromethyl) benzaldehyde;     2,5-difluorobenzaldehyde; 3-fluorobenzaldehyde;     2,6-difluorobenzaldehyde; pentafluorobenzaldehyde;     3,5-difluorobenzaldehyde; 2,4-difluorobenzaldehyde; -   3,4-difluorobenzaldehyde; 3,4,5-trifluorobenzaldehyde;     2,3,4-trifluorobenaldehyde; -   2,4,5-trifluorobenzaldehyde; 2,3-difluorobenzaldehyde;     3-(trifluoromethyl) benzaldehyde; 2-chlorobenzaldehyde;     4-chlorobenzaldehyde; 3-chlorobenzaldehyde; -   2,5-dichlorobenzaldehyde; 3,5-dichlorobenzaldehyde;     2,6-dichlorobenzaldehyde; -   3,4-dichlorobenzaldehyde; 2,4-dichlorobenzaldehyde;     2-chloro-4-fluorobenzaldehyde; 5-chloro-2-fluorobenzaldehyde;     4-chloro-3-fluorobenzaldehyde; 3-chloro-4-fluorobenzaldehyde;     4-chloro-2-fluorobenzaldehyde; 5-bromo-2-chlorobenzaldehyde; -   2-bromo-5-chlorobenzaldehyde; 2-bromo-4-fluorobenzaldehyde;     3-bromo-4-fluorobenzaldehyde; 2-bromo-5-fluorobenzaldehyde;     4-bromo-2-fluorobenzaldehyde; -   4-bromo-3-fluorobenzaldehyde; 3-bromo-2-fluorobenzaldehyde;     3-bromo-2,5-difluorobenzaldehyde; or     2-bromo-4,5-difluorobenzaldehyde.

Examples of halogenated benzoic acids suitable for use in the inventive composite include, but are not limited to, the halogenated benzoic acids corresponding to the above-listed halogenated benzoic aldehydes.

The use of a tracer compound which is non-soluble or substantially non-soluble in the aqueous fracturing fluid assists in preventing the tracer compound from being prematurely leached out of the fractured zone due to the interaction of the tracer composite with the aqueous fracturing fluid when the fracturing fluid return flows back to the wellbore. The leaching out of the tracer compound can result in the loss of the tracer material and can also produce false positive readings for the fractured zone.

As noted above, the solid carrier material used in forming the inventive tracer composite will preferably be non-soluble or substantially non-soluble in water.

In addition, all or substantially all (i.e., at least 95% by weight) of the solid carrier material will preferably be within a particle size range of from 5 to 200 mesh. The particle size of all or substantially all of the solid carrier material will more preferably be within a particle size range of from 5 to 50 mesh and will most preferably be from 8 to 24 mesh. The particle size of the solid carrier material will also preferably be approximately the same as the particle size of the proppant material used in the fracturing fluid.

In addition, the carrier material will preferably have a pore size in the range of from about 20 to about 400 Å (more preferably from about 60 to about 300 Å), a micro porosity of from about 50 to about 200 m² per gram (more preferably about 100 m² per gram), and a specific gravity which is preferably not less than and is more preferably slightly greater than water. The density of the solid carrier material will preferably be in the range of from 1.1 to 3 grams/ml and will more preferably be in the range of from 1.2 to 2 grams/ml. Further, the porous carrier particles will preferably be capable of adsorbing an amount of the tracer of up to 50% by weight of the carrier material and will more preferably be capable of adsorbing an amount of the tracer material in the range of from about 5% to about 30% by weight of the total weight of the inventive tracer composite.

The carrier material will also preferably be a material which will adsorb halogenated benzoic aldehydes of the type described above without the use of a solvent and will provide catalytic sites in the presence of water for converting at least a portion of (preferably at least 50% and more preferably at least 99%) or all of the adsorbed halogenated benzoic aldehyde material to a corresponding benzoic acid. The oxidation of the aldehydes materials to their corresponding benzoic acid forms prevents the tracer material from leaching out of the solid carrier material to any significant degree except when exposed to the increased salinity of the formation water.

The catalyzed oxidation of the adsorbed halogenated benzoic aldehyde material in the presence of water can be illustrated as follows:

Examples of solid carrier materials preferred for use in the tracer composite include, but are not limited to, diatomaceous earth, silica gel, alumina, calcined clay, porous ceramics, and granular carbon. The carrier material will preferably be a granular activated charcoal. Prior to adding the tracer material thereto, the activation of the charcoal will preferably be carried out by heating the charcoal (e.g., at about 150° C. for about 12 hours, preferably under vacuum) to desorb water therefrom. Other carrier materials used in the inventive composite will also preferably be activated in a similar manner prior to the adsorption of the tracer material.

Further, when using silica gel or a porous ceramic as the carrier material, the material will also preferably be silanized by contacting with a silanizing agent such as hexamethyldisilazane, chlorotrimethylsilane, or poly-(dimethylsiloxane) in order to deactivate hydrophilic groups on the surfaces of the porous material. The silanizing agent will preferably be applied in the form of a solvent solution (e.g., an acetonitrile or hexane solution) and the treated carrier material will preferably be drained and dried prior to applying the tracer thereto.

The activation, silanizing, and/or other pre-treatment of the carrier material to cause the carrier material to be more hydrophobic further prevents the tracer material from being prematurely leached out of the fractured zone due to interaction with the aqueous fracturing fluid.

When the tracer material used in the inventive composite is a halogenated benzoic aldehyde of the type described above, the halogenated benzoic aldehyde will typically be a liquid at room temperature and can be adsorbed on the particulate carrier material without the use of a solvent. The halogenated benzoic aldehyde will preferably be sprayed onto the solid carrier material while the particulate carrier material is tumbled, most preferably under vacuum conditions.

When the tracer material used in the inventive composite is or is formed from a halogenated benzoic acid, the tracer material is preferable adsorbed onto the carrier by combining the tracer with a solvent and adding the solution to the carrier, preferably under vacuum conditions and at an elevated temperature (e.g., in a vacuum dryer) in order to evaporate the solvent and leave the tracer material on the external surfaces and the internal pore surfaces of the carrier material. Examples of suitable solvents include, but are not limited to, methanol, hexane, dichloromethane, isopropyl alcohol, and acetone. Preferred application and drying conditions will typically be about 300 millibar and 50° C.

The amount of tracer compound adsorbed onto the solid carrier material will preferably be from about 5% to about 40% by weight of the total weight of the inventive composite. The amount of adsorbed tracer compound will more preferably be from about 10% to about 30% and will most preferably be from about 10% to about 20% by weight of the total weight of the inventive composite.

Although the inventive tracer composite has thus far been described as having only one tracer compound adsorbed onto the solid carrier material, it will be understood that two or more tracer compounds can alternatively be simultaneously or sequentially adsorbed onto the carrier of the inventive composite using the inventive method.

In accordance with the inventive method for fracturing a subterranean formation, an aqueous hydraulic fracturing fluid is injected into a formation zone under pressure. The hydraulic fracturing fluid will typically include a proppant material (i.e., a solid material which is different from the tracer composite provided by the present invention) and can generally also include any number of other fracturing fluid components of the type described above or otherwise used in the art. In addition, in the inventive method, an amount of an inventive tracer composite is also added to all or a portion of the injected fracturing fluid so that the inventive tracer composite is placed and remains in the formation fracture along with the proppant material.

The inventive tracer composite can be added to the fracturing fluid in the blender tub used for forming the proppant slurry. Alternatively, the tracer composite can be combined with water and a sufficient amount of a thickener (e.g., from about 9 to about 10 parts by weight xanthan gum per hundred parts by weight of water) to form an aqueous slurry of the tracer composite which can be injected into the fracturing fluid, preferably via a venturi, as the fracturing fluid is being pumped into the well.

In order to optimize the placement and use of the tracer composite material in the fracture, the tracer composite will preferably be added to and blended with the fracturing fluid so that most of the tracer composite material is placed in the fracture close to the well bore. This is preferably accomplished by blending the tracer composite material with not more than the last ⅔, more preferably not more than the last ½ and most preferably not more than the last ¼, of the proppant material delivered into the fracture.

In addition, the amount of the inventive tracer composite material added to the fracturing fluid will preferably be in the range of from about 0.1 to about 5 kilograms, more preferably from about 1 to about 4 kilograms, per fractured zone (i.e., per fracturing stage).

In a horizontal or other well having multiple fracturing stages, the inventive fracturing procedure described above using the inventive tracer composite can be performed in one, a plurality, or all of the multiple fracturing zones. However, the inventive tracer composites added to the fracturing fluids used to fracture the different formation zones will include different tracers of the type describe above so that (a) the presence of one or more tracers in the product produced from the well will indicate the particular fractured zone or zones from which formation water product was produced and (b) the concentrations of the tracers in the recovered product can be used to determine the amount of formation water being produced from any given zone, or the comparative production of formation water from one zone versus the others.

Because the tracer materials used in the inventive composites are soluble in the higher salinity formation water but are not substantially soluble in the aqueous fracturing fluid, the inventive tracing procedure is effective even during the initial flow back stage of production from the well when the injected fracturing material is or should be flowing back to the well bore. During the flow back stage, the presence of one or more tracers in the recovered fluid indicates which, if any, of the fracturing stages are producing formation water and the quantity or relative rate or amount of formation water which is being produced from each stage versus the other fracturing stages of the formation.

Moreover, at the same time, additional information can be obtained regarding the total amount of water and/or the percentage of fracturing fluid water return versus formation water production for any or each of the fracturing stages by adding an additional tracer to the fracturing fluid which will return with the fracturing fluid flow back or will follow both the fracturing fluid return and production of formation water production from the fracturing stage.

In each embodiment of the inventive fracturing method, the product stream from the well can be sampled as frequently as desired, or continuously analyzed, to determine the presence of any of the tracers from the various fractured zones in the product fluid. By way of example, but not by way of limitation, the presence and concentration of the above described tracer materials in the product sample can be determined using a gas or liquid chromatograph with a mass spectrographic detector, or using other standard laboratory techniques.

It will also be understood that, although the well from which the production samples are taken for tracer analysis will typically be the same well through which the hydraulic fracturing fluids were delivered into the formation, samples for tracer analysis can in addition or alternatively be taken from one or more other wells which are also associated with the fractured formation.

The following example is meant to illustrate, but in no way limit, the claimed invention.

EXAMPLE

A field test involving a single fracturing stage was conducted wherein 2 kg of an inventive tracer composite for tracing the recovery of formation water was added to the concluding half of the fracturing fluid injected into the formation. The inventive tracer composite used in this test was formed of benzoic aldehyde on a granular activated charcoal support. The amount of benzoic aldehyde adsorbed on the activated charcoal support was 20% by weight of the total weight of inventive tracer composite.

In addition, 1 kg of an FFI fracturing fluid tracer available from Spectrum Tracer Services was also added to the fracturing fluid during injection using a peristaltic pump.

After fracturing, samples of the fluid produced from the well were taken over a two month period and were analyzed for the presence and concentration of the formation water tracer, the FFI tracer, and salt.

The sample progression showed a gradual increase in the salinity of the recovered fluid over the sample period, thus indicating an increase in the production of formation water. This increase in salinity was accompanied by a corresponding increase in the concentration of the formation water tracer and a decrease in the concentration of the FFI fracturing fluid tracer in the recovered fluid, which indicated that the formation water tracer was being released and recovered at a greater rate and concentration in correspondence with the increased salinity of the recovered fluid and the increase production of formation water from the formation.

Thus, the present invention is well adapted to carry out the objectives and attain the ends and advantages mentioned above as well as those inherent therein. While presently preferred embodiments have been described for purposes of this disclosure, numerous changes and modifications will be apparent to those in the art. Such changes and modifications are encompassed within this invention as defined by the claims. 

What is claimed is:
 1. A tracer composite for use in tracing production of formation water, comprising: a solid carrier material which is substantially non-soluble in water; and a tracer on the solid carrier material; wherein the tracer is held on the solid carrier material to substantially prevent the tracer from being eluted from the solid carrier material at a detectable level in water having a salinity level of less than 1 part per thousand by weight but permit the tracer, at least when the salinity level of the water reaches a value of 5 parts per thousand by weight, to be eluted from the solid carrier material at detectable levels which increase as the salinity level of the water increases; and wherein the solid carrier material comprises catalytic sites that, in the presence of water, convert aldehydes adsorbed on the solid carrier material to acids.
 2. The tracer composite of claim 1, wherein the tracer comprises a halogenated benzoic acid adsorbed to the solid carrier material.
 3. The tracer composite of claim 2, wherein at least a portion of the halogenated benzoic acid adsorbed to the solid carrier material has been converted from a halogenated benzoic aldehyde by catalytic sites of the solid carrier material during manufacture of the tracer composite.
 4. The tracer composite of claim 3, wherein at least 50% of the halogenated benzoic aldehyde adsorbed on the solid carrier material has been converted to the halogenated benzoic acid.
 5. The tracer composite of claim 1, wherein the solid carrier comprises diatomaceous earth, silica gel, alumina, calcined clay, porous ceramics, or granular carbon.
 6. The tracer composite of claim 5, wherein the solid carrier comprises silica gel or a porous ceramic.
 7. The tracer composite of claim 6, wherein the solid carrier material is silanized.
 8. The tracer composite of claim 6, wherein the solid carrier material has been silanized by contacting with a silanizing agent comprising hexamethyldisilazane, chlorotrimethylsilane, or poly-(dimethylsiloxane).
 9. The tracer composite of claim 6, wherein the silanizing agent is delivered in a solvent comprising acetonitrile or hexane solution.
 10. The tracer composite of claim 5, wherein the hydrophilic groups on surfaces of the solid carrier material have been deactivated.
 11. The tracer composite of claim 1, wherein the tracer adsorbed onto the solid carrier material is about 10% to about 30% by weight of the total weight of the tracer composite.
 12. A method of manufacturing a tracer composite, comprising: contacting a solid carrier material which is porous and substantially non-soluble in water with a tracer to adsorb the tracer onto the solid carrier material; wherein the tracer is held on the solid carrier material to substantially prevent the tracer from being eluted from the solid carrier material at a detectable level in water having a salinity level of less than 1 part per thousand by weight but permit the tracer, at least when the salinity level of the water reaches a value of 5 parts per thousand by weight, to be eluted from the solid carrier material at detectable levels which increase as the salinity level of the water increases.
 13. The method of claim 12, further comprising silanizing the solid carrier material prior to contacting the silanized solid carrier material with the tracer.
 14. The method of claim 13, further comprising draining and drying the silanized solid carrier material prior to contacting the silanized solid carrier material with the tracer.
 15. The method of claim 13, wherein the silanizing comprises contacting the solid carrier material with a silanizing agent comprising hexamethyldisilazane, chlorotrimethylsilane, or poly-(dimethylsiloxane).
 16. The method of claim 15, wherein the silanizing agent is delivered in a solvent comprising acetonitrile or hexane solution.
 17. The method of claim 12, wherein the tracer comprises a halogenated benzoic aldehyde that is liquid at room temperature, and is adsorbed onto the solid carrier material without use of a solvent.
 18. The method of claim 17, wherein the tracer is sprayed onto the solid carrier material while the solid carrier material is tumbled under vacuum conditions.
 19. The method of claim 12, wherein the tracer comprises a halogenated benzoic acid and is adsorbed onto the solid carrier material by combining the tracer with a solvent, contacting the tracer-containing solvent with the solid carrier material, and evaporating the solvent to leave the tracer on surfaces of the solid carrier material.
 20. The method of claim 19, wherein the solvent comprises methanol, hexane, dichloromethane, isopropyl alcohol, or acetone, and wherein the evaporating is conducted under vacuum conditions. 